This invention pertains to digital communication systems, and more particularly is concerned with clocking means to recover data in such systems.
Digital systems require a clock signal for data recovery. The maximum possible frequency of the data stream is for the condition of alternating ones and zeros (i.e., 0101010. . . ). As a result, the clock frequency is exactly twice that of maximum data rate. In some systems the clock signal is sent with the data. Such a system must therefore be designed to operate at twice the speed of the data stream so as to carry the clock signal. For example, a data rate of 150 Mb/s requires the system to support a 300 Mb rate clock signal.
An object of this invention is to provide means to double the transmitted clock frequency to allow data to be sent at the maximum rate supported by the system.